Effect Of Salt And Osmotic Stress On Seed Germination And Seedling Growth Of Melilotoides Ruthenica (L.) Sojak

Drought and salt stress are the most factors limiting development of animal husbandry. There have been many studies on stressed physiology of pasture crops, but little has been done on Melilotoides ruthenica (L.)Sojak, which is a native legume plant occurred widely in semiarid area in northern China and characterized by strong tolerance to drought and salinity. In this thesis, I studied the role of polymines and ethylene in seed germination and seedling growth under conditions of salt (NaCl) and osmotic (polyethyleneglycol PEG6000) stress. The main results was followed,1. Seed germination rate of M. ruthenica was inhibited by NaCl in a concentration-dependent manner. Spermine, but not sperdine, ameliorated the NaCl-induced reduction in seed germination rate. The ameliorative effect of spermine on seed germination may occur through interation with seed coats of M. ruthenica seeds.2. Salt stress reduced the growth of M. ruthenica seedlings. Application of silicon (Si) increased the biomass and proline contents, and decreased activities of antioxidant enzymes of SOD, and stimulated activities of antioxidant enzymes of POD, and improved root hydraulic conductivity (Lpr). These results indicate that Si can improve growth of M. ruthenica seedlings exposed to salt stress.3. Osmotic stress evoked ethylene production in roots of M. ruthenica, and reduced activities of SOD, POD and CAT, and increased the electrical conductivity (EC) and contents of malondialdehyde (MDA) and proline (Pro). Cobalt (Co²⁺), which is an inhibitor of ethylene synthesis, alleviated the osmotic-idnuced changes in the above mentioned physiological paramenters, thus protecting M. ruthenica seedlings from osmotic stress by minimaizing osmotic stress-induced oxidative stress. These results showed increaseed production of ethylene may be an important trigerr to induce inhibtion of M. ruthenica seedling growth under conditions of osmotic stress.